Configuring Power over Ethernet

Note Before reading this chapter, read the "Preparing for Installation" section of the Catalyst 4500 Series Installation Guide. It is important to ensure that your installation site has enough power and cooling to accommodate the additional electrical load and heat introduced by PoE.

This chapter describes how to configure Power over Ethernet (PoE) on the Catalyst 4500 series switch.

Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Overview

The Catalyst 4500 series switch provides support for Power over Ethernet (PoE) for both Cisco Prestandard PoE and the IEEE 802.3af standard (ratified in 2003). PoE is supported by all Catalyst 4500 series chassis and requires a PoE module and power supply. The amount of PoE power available depends on the PoE capabilities of individual power supplies. Support for PoE enables the system to power inline devices, such as IP phones, IP video phones, and wireless access points over standard copper cabling (Category 5, 5e, or 6 cabling).

In addition, with PoE, you do not need to provide wall power for each PoE enabled device. This eliminates the cost for additional electrical cabling that would otherwise be necessary for connected devices. Moreover, PoE enables you to isolate critical devices on a single power system, enabling the entire system to be supported by UPS backup.

You typically deploy a Catalyst 4500 series switch in one of two deployment scenarios. The first scenario is data-only, which requires power to operate the switch and the associated modules. The second scenario supports data and PoE (also termed "inline power") for deployments where the attached device derives power from the Ethernet port.

Catalyst 4500 series switches can sense if a powered device is connected to a PoE module. They can supply PoE to the powered device if there is no power on the circuit. (If there is power on the circuit, the switch does not supply it.) The powered device can also be connected to an AC power source and supply its own power to the voice circuit.

Note You should select the amount of PoE desired using the Cisco Power Calculator:

http://tools.cisco.com/cpc/

Hardware Requirements

To power a device using PoE, your chassis must use at least one of the power supplies listed in Table 11-1, and connect the device to at least one of the switching modules listed in Table 11-1.

Table 11-1 Hardware Requirements

Switching Modules

Power Supplies

WS-X4148-RJ45V

PWR-C45-1300ACV=

WS-X4224-RJ45V

PWR-C45-1400DCV=

WS-X4248-RJ21V

PWR-C45-2800ACV=

WS-X4248-RJ45V

PWR-C45-4200ACV=

WS-X4505-GB-T

WS-X4524-GB-RJ45V

WS-X4548-GB-RJ45V

WS-X4648-RJ45V-E

WS-X4648-RJ45V+E

Power Management Modes

If your switch has a module capable of providing PoE to end stations, you can set each interface on the module to automatically detect and apply PoE if the end station requires power.

The Catalyst 4500 series switch has three PoE modes:

•auto—PoE interface. The supervisor engine directs the switching module to power up the interface only if the switching module discovers the phone and the switch has enough power. You can specify the maximum wattage that is allowed on the interface. If you do not specify a wattage, then the switch will deliver no more than the hardware-supported maximum value. This mode has no effect if the interface is not capable of providing PoE.

•static—High priority PoE interface. The supervisor engine preallocates power to the interface, even when nothing is connected, guaranteeing that there will be power for the interface. You can specify the maximum wattage that is allowed on the interface. If you do not specify a wattage, then the switch preallocates the hardware-supported maximum value. If the switch does not have enough power for the allocation, the command will fail. The supervisor engine directs the switching module to power up the interface only if the switching module discovers the powered device.

•never—Data interface only The supervisor engine never powers up the interface, even if an unpowered phone is connected. This mode is only needed when you want to make sure power is never applied to a PoE-capable interface.

The switch can measure the actual PoE consumption for an 802.3af-compliant PoE module, and displays this in the show power module command.

PoE consumption cannot be measured on the WS-X4148-RJ45V PoE module. Therefore, for all PoE calculations, the PoE consumption on this module is presumed to be equal to its administrative PoE.

For most users, the default configuration of "auto" works well, providing plug and play capability. No further configuration is required. However, to make an interface higher priority or data only, or to specify a maximum wattage, perform this task:

The auto keyword sets the interface to automatically detect and supply power to the powered device. This is the default configuration.

The static keyword sets the interface to higher priority than auto.

If necessary, you can use the max keyword to specify the maximum wattage allowed on the interface (4000 to 15400 milliwatts for most switching modules. As of Cisco IOS release 12.2(44)SG the WS-X4648-RJ45V+E can support up to 20 W available per port and the WS-X4648-RJ45V-E will support up to 20 W. For more information, see "Enhanced Power PoE Support on the E-Series" on page 12).

Use the never keyword to disable detection and power for the PoE capable interface.

Step 3

Switch(config-if)# end

Exits configuration mode.

Step 4

Switch# show power inline {fastethernet |
gigabitethernet} slot/port

Displays the PoE state for the switch.

Note If you set a non-PoE-capable interface to automatically detect and apply power, an error message indicates that the configuration is not valid.

The following example shows how to set the Fast Ethernet interface 4/1 to automatically detect PoE and send power through that interface, and to verify the PoE configuration:

The following example shows how to configure an interface so that it never supplies power through the interface:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# interface fastethernet 5/2

Switch(config-if)# power inline never

Switch(config-if)# end

Switch#

Intelligent Power Management

All Catalyst 4500 PoE-capable modules use Intelligent Power Management to provide power on each interface. When a powered device (PD) is attached to a PoE-capable port, the port will detect the PD and provision power accordingly. If a Cisco PD is used, the switch and PD negotiate power using CDP packets to determine the precise amount of power needed by the PD. If the PD is 802.3af compatible, the difference between what is mandated by the 802.3af class and what is actually needed by the PD is returned to the power budget for use by additional devices. In this way, power negotiation enables customers to stretch their power budget and use it more effectively.

Power negotiation also enables the interoperability of newer Cisco powered devices with older legacy PoE-capable ports from Cisco. Newer Cisco PDs do not consume more than what the switch port can provide.

Configuring Power Consumption for Powered Devices on an Interface

By default, when the switch detects a powered device on an interface, it assumes the powered device consumes the maximum the port can provide (7 W on a legacy Power over Ethernet (PoE) module and 15.4W on the IEEE PoE modules introduced in Cisco IOS Release 12.2(18)EW). Then, when the switch receives a CDP packet from the powered device, the wattage automatically adjusts downward to the specific amount required by that device. Normally, this automatic adjustment works well, and no further configuration is required or recommended. However, you can specify the powered device's consumption for the entire switch (or for a particular interface) to provide extra functionality from your switch. This is useful when CDP is disabled or not available.

Note When manually configuring the consumption for powered devices, you need to account for the power loss over the cable between the switch and the powered device.

To change the power consumption for the entire switch, perform this task:

Command

Purpose

Step 1

Switch(config)# [no] power inline consumption
defaultmilli-watts

Sets the PoE consumption (in milliwatts) of all powered devices connected to the switch. The power consumption can range from 4000 to 15,400.

To re-enable the automatic adjustment of consumption, either use the no keyword or specify 15,400 milliwatts.

Step 2

Switch(config)# end

Exits configuration mode.

Step 3

Switch# show power inline consumptiondefault

Displays the administrative PoE consumption of powered devices connected to the switch. The administrative PoE is not the measured PoE value.

This example shows how to set the default PoE consumption of all powered devices connected to the switch to 5000 milliwatts, and to verify the PoE consumption:

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# power inline consumption default 5000

Switch(config)# end

Switch# show power inline consumption default

Default PD consumption : 5000 mW

Switch#

To change the power consumption of a single powered device, perform this task:

Command

Purpose

Step 1

Switch(config)# interface {fastethernet |
gigabitethernet} slot/port

Selects the interface to configure.

Step 2

Switch(config-if)# [no] power inline
consumptionmilli-watts

Sets the PoE consumption (in milliwatts) of the powered device connected to a specific interface. The power consumption can range from 4000 to 15,400.

To re-enable the automatic adjustment of consumption, either use the no keyword or specify 15,400 milliwatts.

This example shows how to set the PoE consumption to 5000 milliwatts for interface gi 7/1 regardless what is mandated by the 802.3af class of the discovered device, or by any CDP packet received from the powered device. This example also verifies the PoE consumption on interface gi 7/1.

The following output displays the inital power consumption of the interface.

Displaying the Operational Status for an Interface

Each interface has an operational status which reflects the PoE status for an interface. The operational status for an interface is defined as one of the following:

•on—Power is supplied by the port.

•off—Power is not supplied by the port. If a powered device is connected to an interface with external power, the switch does not recognize the powered device. The "Device" column in the show power inline command displays as n/a.

•Power-deny—The supervisor engine does not have enough power to allocate to the port, or the power that is configured for the port is less than the power required by the port; power is not being supplied by the port.

•err-disable—The port is unable to provide power to the connected device that is configured in static mode.

•faulty—The port failed diagnostics tests.

You can use the show power inline command to view the operational status for an interface.

This example shows how to display the operational status for all interfaces on module 3.

Displaying the PoE Consumed by a Module

The switch can measure the actual PoE consumption for an 802.3af-compliant PoE module, and it displays the measured PoE in both the show power module and show power detail commands.

For all PoE calculations, the PoE consumption on the WS-X4148-RJ45V module is presumed to be equal to its administrative PoE.

The 802.3af-compliant PoE modules can consume up to 20 W of PoE to power FPGAs and other hardware components on the module. Be sure to add at least 20 W to your PoE requirements for each 802.3af-compliant PoE module to ensure that the system has adequate power for the PDs connected to the switch.

The example below displays the PoE consumption for an 802.3af-compliant module using the show power module command.

The "Inline Power Oper" column displays the amount of PoE consumed by the powered devices that are attached to the module, in addition to the PoE consumed by the FPGAs and other hardware components on the module. The "Inline Power Admin" column displays only the amount of PoE allocated by the powered devices attached to the module.

Note The operating PoE consumption for an 802.3af-compliant module can be non-zero, even when there are no powered devices attached to the module, because of the PoE consumed by FPGAs and other hardware components on the module. In addition, the operating PoE can vary due to fluctuations in the PoE consumed by the hardware components.

Switch# show power module

Watts Used of System Power (12V)

Mod Model currently out of reset in reset

---- ----------------- --------- ------------ --------

1 WS-X4013+TS 330 330 330

2 WS-X4548-GB-RJ45V 60 60 20

3 WS-X4548-GB-RJ45V 60 60 20

-- Fan Tray 30 -- --

----------------------- --------- ------------ -------

Total 480 450 370

Watts used of Chassis Inline Power (-50V)

Inline Power Admin Inline Power Oper

Mod Model PS Device PS Device Efficiency

---- ----------------- ---------------- ---------------- ----------

2 WS-X4548-GB-RJ45V 138 123 73 65 89

3 WS-X4548-GB-RJ45V 0 0 22 20 89

----------------------- ---------------- ---------------- ----------

Total 138 123 95 85

Watts used of Module Inline Power (12V -> -50V)

Inline Power Admin Inline Power Oper

Mod Model PS Device PS Device Efficiency

---- ----------------- ---------------- ---------------- ----------

1 WS-X4013+TS 128 128 63 63 100

----------------------- ---------------- ---------------- ----------

Switch#

The example below displays the PoE consumption for an 802.3af-compliant module using the show power detail and show power inlinecommands.

The "Inline Power Oper" column displays the amount of PoE consumed by the powered devices that are attached to the module, in addition to the PoE consumed by the FPGAs and other hardware components on the module. The "Inline Power Admin" column displays only the amount of PoE allocated by the powered devices attached to the module.

Enhanced Power PoE Support on the E-Series

Both the WS-X4648-RJ45V-E and WS-X4648-RJ45V+E switching modules support IEEE 802.3af power over Ethernet as well as the Cisco proprietary Inline Power standard, and as of Cisco IOS release 12.2(44)SG the WS-X4648-RJ45V+E can also support the IEEE 802.3at standard, with up to 20 W available per port. The WS-X4648-RJ45V-E will support up to 20 W as of Cisco IOS release 12.2(44)SG. For these switching modules, the valid milliwatt ranges for the power inline command are increased appropriately for the module.

In typical applications, the default power inline configurations are sufficient and no additional configuration is required even for high power consumption Cisco powered devices, for example a Cisco AP1250 Wireless Access Point. When a high power consumption device is attached to a port on a WS-X4648-RJ45V-E or WS-X4648-RJ45V+E, the switch and device negotiate power using CDP packets to automatically determine the extended amount of power needed by the device.

Depending on the deployment requirements and design, a specific configuration can be entered with the power inline command. This example shows how to pre-allocate Power over Ethernet allocation to 16500 mW for Gigabit Ethernet interface 2/1 regardless of what is mandated either by the 802.3af class of the discovered device or by any CDP packet that is received from the powered device: